The present invention relates to a railway axle of traditional type, into the structure of which is integrated a detector for sensing the speed of rotation of the wheel (in the case of bogies having independent wheels) or of the wheels (in the case of traditional rigid bridge bogies) fixedly mounted to the axle.
It is known that the problem of preventing the wheels from locking during braking, with consequent loss of adhesion, is today encountered not only on road vehicles, but also on modern high speed trains; therefore, antilock braking systems, the so-called ABS devices, have been developed, which are usable on railway bogies with which engines and wagons are equipped. As is known, such bogies usually comprise a pair of axles, each of which supports a pair of wheels; in rigid bridge bogies the two wheels are carried by a single shaft, one on each end, and the shaft is carried freely rotatably by respective supports connected by means of a suspension system having shock absorbing arms, to the supporting structure of the bogie, in turn connected to the wagon or engine. In independent wheel bogies, on the other hand, each wheel of each axle is supported by its own shaft, mounted so as to project through a respective support; these are carried by suspension arms as in the preceding case.
In both types of bogie the speed of rotation of the wheel is detected by means of a sensor disposed in a fixed position in front of a toothed wheel, known as a "phonic wheel" or "impulse ring", made of magnetic material and fitted to the shaft: by rotating the shaft, a succession of voids and solid parts determined by the presence of the teeth on the phonic wheel pass in succession in front of the coil and cause the creation of a variable electrical signal across its terminals, the frequency of which signal is proportional to the number of teeth which transit in front of the sensor in a unit of time and, therefore, to the speed of rotation of the wheel or wheels fitted to the shaft together with the phonic wheel. The signal generated by the sensor is then processed by an electronic central processing unit which, by comparing it with signals generated by the other wheels of the bogie, is able to detect wheel-lock phenomena during braking and, consequently, to control the braking device in a suitable manner.
The arrangement described is not, however, entirely free from disadvantages. In particular, the sensors and the associated phonic wheels are bulky and difficult to adjust; assembly is therefore onerous in that it is necessary to ensure a perfect centering, between the sensor, usually carried by the closure cover for the shaft bearing housing, and the phonic wheel, carried by this latter, otherwise the system performs poorly; finally, the sensors have a low sensitivity at low speed so that the ABS system of the train does not detect speeds below five to seven Km/h.